# Arithmetic series

An

**arithmetic series** is the sum of a

sequence of

numbers in which the difference between each number and its predecessor is a constant. The sum

*S* of the first

*n* values of a finite sequence is given by the formula:

*S* = ½*n*(*a*_{1} + *a*_{n})

where

*a*_{1} is the first term and

*a*_{n} the last.